Childhood maltreatment, in the form of abuse and neglect, is a major public health problem. Maltreated children have elevated rates of internalizing psychopathology and are at high risk for a broad range of adverse outcomes. Infants and young children are at the greatest risk of maltreatment and may have the most severe squeal of maltreatment. Insofar as primary prevention of maltreatment is often not feasible, the identification of factors that influence positive outcomes in maltreated children is critically important. Genetic risk and protective factors appear to play an important role in the behavioral squeal of childhood maltreatment. A number of recent studies have identified specific genes that interact with childhood adversity to produce risk for major depression and anxiety-related traits in adults and children. These include genes that regulate monoamine neurotransmission and neuroendocrine function. One likely mechanism of gene-environment interactions is that risk genes may confer sensitivity to stress, possibly through altered functioning of the HPA axis. A substantial body of evidence documents dysregulation of HPA axis function in animal models of early adversity. A growing body of research in children and adults with a history of early maltreatment provides evidence of dysfunction of this stress system (which may be reflected in exaggerated or attenuated cortisol responses). Converging lines of evidence from preclinical and clinical studies indicate that excessive activation of the HPA axis may be toxic and result in alterations of brain structure and function in circuitry involved in major depression and other disorders. In addition to enduring neuroendocrine effects of early-life stress, such HPA axis hyperactivity may in part result from gene variants involved in the regulation of this stress axis. The goal of the present application is to identify genetic and neuroendocrine predictors of behavior problems and psychopathology in maltreated preschoolers. Genes that regulate monoamine or HPA axis function will be examined based on involvement in neural pathways implicated in these behavioral problems as well as prior empirical associations with internalizing disorders and maltreatment. Further, we seek to determine whether alterations in HPA axis function mediate these relationships. A follow-up assessment will examine prospective relationships between these biomarkers and behavioral outcomes as well as the stability of associations of neuroendocrine activity with behavior. These results should provide valuable information regarding the development of affective and behavioral problems in maltreated children that could guide treatment and prevention efforts as well as direction for future clinical research efforts.